Heat Exchanger

ABSTRACT

The invention relates to a heat exchanger, particularly in tube bundle-type, panel-type or plate-type design. The heat exchanger has a housing inside of which a number of flow channels are formed for a primary flow and a secondary medium, and the housing has a sandwich design.

The invention relates to a heat exchanger of a tube-bundle type ofconstruction or of a disk type of construction according to preamble ofclaim 1.

On account of the ever increasing loads with regard to pressure andtemperature, ever increasing requirements with regard to the strength ofheat exchangers are being imposed. A main problem in this case is thepressure difference between the primary medium in the flow passagesprovided for it in the heat exchanger and the secondary medium in therespectively adjacent flow passages. The separation between primarymedium and secondary medium is normally effected by relatively thinplate walls, which on their own cannot bear the pressure differencebetween the two media, so that greater wall thicknesses are required,which, however, entail disadvantages, for example with regard to thematerial and production costs and with regard to the overall weight.

The heat exchanger is normally constructed in such a way that the flowpassages of the primary and secondary medium alternate, so that thepressure level of the other medium is present on both sides of the innerflow passages. By introduction of supporting structures into a flowpassage, said flow passage can be supported against excess pressure fromthe other side. Since the pressure on both sides of the passage is thesame, the opposite flow passage walls support one another via thesupporting structures. If supporting structures are introduced into bothflow passages, that is to say into the flow passages of the primarymedium and the flow passages of the secondary medium, all the flowpassages are supported against excess pressure from the outside, and theheat exchanger is therefore designed for excess pressure of the primarymedium relative to the secondary medium, and vice versa. If thesupporting structure is firmly connected to the flow passage walls, itprovides stiffening not only against excess pressure from outside as aresult of the support but also against excess pressure inside the flowpassage by acting as a tie rod between the two opposite flow passagewalls. Rib structures, supporting plates or supporting studs/beads arenormally used.

An example of a known tube-bundle type of construction with stud supportis shown in FIGS. 2 a and 2 b. In the interior of the heat exchanger101, such stiffening with studs 110 leads to a structure which is verystable under pressure, since a symmetrical load case with equalpressures is present at respectively opposite flow passage walls.However, the outer flow passages present a problem, since only theambient pressure or the housing wall 102, which itself is not supported,opposes the pressure on the outside of the flow passages. There istherefore a risk of damage to the outermost flow passage as a result ofthe pressure difference. Furthermore, the outermost passage may inflateas a result of the high internal pressure, so that the shape changes andthe flow passage is displaced and/or is no longer supportedsymmetrically, which has an effect on the adjacent flow passages, sothat the entire heat exchanger including the housing “inflates”. Onaccount of expansions, the service life of the heat exchanger may beconsiderably reduced. To increase the stability, the housing 102 isdesigned to be relatively thick, which, inter alia, leads to highweight.

In order to prevent inflation, for an oil cooler of a disk type ofconstruction, provision is made in DE 197 11 258 C2 for a base plate ofthick design to bear against the outermost disk, this base plate, apartfrom the thickness, corresponding in its shape approximately to theshape of the outermost disk. However, this base plate has thedisadvantage of high weight.

The object of the invention is to provide an improved heat exchanger.

This object is achieved by a heat exchanger having the features of claim1. Advantageous configurations are the subject matter of the subclaims.

A heat exchanger, in particular of a tube-bundle, plate or disk type ofconstruction, is provided according to the invention, the heat exchangerhaving a housing in which a plurality of flow passages for a primarymedium and a secondary medium are formed, and the housing is formed witha sandwich type of construction. The heat exchanger in this case is anexhaust-gas cooler. Instead of an exhaust-gas cooler, any other desiredheat exchanger of corresponding construction, for example acharge-air/cooling-medium cooler or an oil cooler, may also be used.

The housing is preferably formed by at least two, preferably threeplates, the outer surface of the outer plate forming the housing outersurface. The inner plate is preferably at a distance from the outerplate, a central plate which has a rib structure preferably beingarranged between the outer plate and the inner plate. Instead of a ribstructure, other structures, for example studs/beads, keeping the twoplates at a distance apart are also possible.

The plates are preferably brazed to one another. The brazing in thiscase may be effected in a single operation, for which purpose the platesare appropriately prepared before assembly.

Preferably arranged in the housing on the inside of the inner plate aretube bundles, plates or disk stacks, which serve for the heat exchangebetween the two operating media.

A flow passage for one of the operating media is preferably providedbetween the outer plate and the inner plate, so that this operatingmedium is also located outside the region in which the actual heatexchanger structures, such as tube bundles for example, are provided anda corresponding pressure prevails.

Due to the configuration of the housing according to the invention,markedly smaller material thicknesses can be used instead of a singlehousing wall of considerable thickness, at roughly the same costs, saidmaterial thicknesses exhibiting increased material strength in such aconstruction. At comparable strength values, the structural weight canbe markedly reduced compared with conventional housings. Furthermore, inthe unbrazed state, the components are comparatively flexible and caneasily be worked, since no beading or the like is necessary. Due to theflat surfaces of relatively large area, the connection to the adjacentcomponents in the housing, for example by brazing, is assisted. Ifrequired, gap dimensions which ensure planar brazing of the two outerplates with the rib structure inbetween to form the housing can be setwith low clamping forces and low forces due to weight during the brazingprocess. It is only in the brazed state that a structure of high bendingstrength is obtained.

Possibly advantageous is a housing having precisely two plates, of whichat least one is provided in an especially preferred manner with spacerssuch as ribs, webs, corrugations, studs or the like. A reduction in thenumber of plates simplifies the production of the heat exchanger.

According to a preferred configuration, simplification of the productioncan likewise possibly be achieved by the housing being formed with asandwich type of construction only on two sides or in two housingregions opposite one another.

The invention is explained in detail below with reference to anexemplary embodiment with variant, and partly with reference to thedrawing, in which:

FIG. 1 shows a section, with only partly shown inner structure, througha heat exchanger according to the invention, and

FIGS. 2 a, b each show a cut-away section in different directionsthrough a heat exchanger of a tube-bundle type of construction with studsupport according to the prior art.

A heat exchanger 1 serving as exhaust-gas cooler 1 has a housing 2 whichis formed by a sandwich structure consisting of a plurality of plates 3,4 and 5. The outer plate 3 forms with its outer surface the outersurface of the heat exchanger 1.

The outer plate 3 has a tub-shaped region 3′ and a lid 3″ closing saidtub-shaped region 3′. The central plate 4 provided with a rib structureand, on the inner side thereof, the inner plate 5 are arranged so as torun in each case parallel to the outer plate 3, that is to say both inthe tub-shaped region 3′ and in the region of the lid 3″, and are brazedto one another, the plates 4 and 5 being designed to be shorter than theouter plate 3.

The tube bundles 6 of the exhaust-gas cooler are arranged on the insideof the inner plate 5. In this case, the outermost tube of the tubebundle 6 in each case bears directly against the inner surface of theinner plate 5 and is brazed to the latter. The joining or brazing of theheat exchanger 1 is effected in one operation in a manner known per se.

A first flow passage, in the present case for the medium to be cooled,namely the exhaust gas (primary medium), is formed by the interior spaceof the tube bundles 6, and a second flow passage, in the present casefor the cooling medium (secondary medium), is formed by the intermediatespaces between the tube bundles 6. The intermediate space of the housing2, which intermediate space is of hollow design on account of the ribstructure of the central plate 4, is assigned to the second flow passageas outermost region of the same, so that a corresponding pressureprevails here too.

According to a variant (not shown in the drawing), a stack of disk pairsis arranged in the interior of a housing of corresponding multi-piecedesign instead of the tube bundles 6, these disk pairs forming the firstflow passage in their interior and the second flow passage in theintermediate spaces and in the intermediate spaces relative to theoutermost plate.

LIST OF DESIGNATIONS

-   1, 101 Heat exchanger-   2, 102 Housing-   3 Outer plate-   3′ Tub-shaped region-   3″ Lid-   4 Central plate-   5 Inner plate-   6 Tube bundle-   110 Stud

1. A heat exchanger, in particular of a tube-bundle, plate or disk typeof construction, the heat exchanger having a housing in which aplurality of flow passages for a primary medium and a secondary mediumare formed, wherein the housing is formed, at least in regions, inparticular so as be essentially continuous, with a sandwich type ofconstruction.
 2. The heat exchanger as claimed in claim 1, wherein thehousing of sandwich type of construction is formed by at least twoplates, the outer surface of the outer plate forming the housing outersurface.
 3. The heat exchanger as claimed in claim 1, wherein thehousing of sandwich type of construction is formed by at least twoplates, the inner plate being at a distance from the outer plate formingthe housing outer surface.
 4. The heat exchanger as claimed in claim 1,wherein the housing of sandwich type of construction comprises a ribstructure formed by a central plate, this rib structure being arrangedbetween an outer plate and an inner plate.
 5. The heat exchanger asclaimed in claim 4, wherein the rib structure is brazed or welded inplace between the outer plate and the inner plate.
 6. The heat exchangeras claimed in claim 1, wherein, in the housing of sandwich type ofconstruction, a flow passage for one of the operating media is providedbetween an outer plate and an inner plate.
 7. The heat exchanger asclaimed in claim 1, wherein, in the housing of sandwich type ofconstruction, tube bundles, plates or disk stacks are arranged on theinside of an inner plate.
 8. The heat exchanger as claimed in claim 1,wherein the housing, at least in regions, has precisely two plates whichare provided in particular with spacers such as ribs, webs,corrugations, studs or the like.
 9. The heat exchanger as claimed inclaim 1, wherein the housing is formed in a sandwich type ofconstruction in each case in housing regions arranged opposite oneanother, in particular in two housing regions.
 10. The use of a heatexchanger as claimed in claim 1 as an exhaust-gas cooler, acharge-air/cooling-medium cooler or an oil cooler.